000
FXUS61 KBOX 171052
AFDBOX
Area Forecast Discussion
National Weather Service Taunton MA
652 AM EDT Sat Mar 17 2018
.SYNOPSIS...
Mainly dry but unseasonably cold weather will continue into
early next week. A multi-part storm system moves to the Mid
Atlantic states midweek. This system may affect parts of
Southern New England during midweek, but it is also possible the
storm stays to our south. Currently there is low confidence on
the eventual behavior of this storm. High pressure builds with
drier weather Friday.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
645 AM Update...
Mostly clear skies across Southern New England. But satellite
imagery does note a patch of clouds off the Cape and Islands,
and a second area of clouds over VT and Northern NY, the latter
showing mainly mid-level clouds.
No changes in conditions, with a Northwest upper jet diving
across New England. This along with 7C/km lapse rates should
generate lift. Daytime sunshine will support mixing through the
lower layers, and draw strong wind gusts to the surface. The
result will be cloud development during the morning,
temperatures climbing into the 30s, and gusts to 35 mph. No
significant changes to the forecast planned at this time.
Previous discussion...
WV imagery suggests core of a strong vort-max and attendant H5
cutoff is rotating through central Quebec. Meanwhile slight warm
advection to the has allowed heights to build overnight. This
has lead to mainly clear conditions, except where a very narrow
band of moisture, between H85 and H7 has led to some SC enhanced
by higher terrain of W MA. This squeeze play has allowed for
some continued cold advection near the surface, enhanced by a
stronger height rise-fall couplet and resultant winds.
Otherwise, the vort-max moves through N New England through the
day, leading to a kink in the MSLP fields mid day. This implies
convergence at the sfc. Noting also through the morning that
continued low-mid lvl cold advection will lead to enhanced lapse
rates from the sfc to the top of the mixed layer (around H75)
near 7C/km. The lake enhanced moisture field between H85 and H7
rests around the top of this mixed layer. Based on all of this,
cannot rule out a brief snow shower or even squall (thanks to
gusty winds 25-35 mph remaining an issue). Otherwise, flurries
or sprinkles. The limiting factor will be the moisture as it
remains low and only in the layer mentioned above. Therefore,
little to no accumulation is expected, but a few spots on the
grass are possible. This risk ends by late afternoon/evening as
height rises lead to stronger subsidence, both eroding the
moisture layer and supressing any weak lift.
Highs will be limited to the 30s for the most part, as H85 temps
remain at or below -11C all day, and even if mixing reaches
higher it would be limited by the continued lower lvl cold
advection.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/...
Overnight...
With rising heights aloft, subsidence will lead to clearing and
finally slacken the sfc pres gradient. This suggests clearing
skies and a weak enough pres gradient for some radiational
cooling. This will allow min temps to drop into the teens and
even single digits at the obs sites normally prone to
decoupling. Otherwise a dry ngiht, one of the colder nights in
recent past.
Sun...
A stretched vort-max pivots through the SW flow aloft, on the W
periphery of a longwave trof across the Maritimes. Once again,
the majority of the column is moisture starved, but with weak
lift and NW flow some CAA SC is likely throughout the day, along
with a risk for ocean enhancement along the Cape. Mainly dry
otherwise. NW winds, but generally weaker than previous days as
the core of the sfc pres gradient change is to the E.
&&
.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Big Picture...
Closed low over the Maritimes slowly ejects northeast. This keeps a
cyclonic flow over New England early in the week. Southern jet
stream remains in place most of the period with one shortwave moving
east to the Mid Atlantic coast Tuesday and a second digging in over
the Midwest Wednesday. This sets up a complicated flow to our south
that generates multiple weather systems. These could easily pass to
our south, or one of them may turn north and bring pcpn to Southern
New England.
Run-to-run trends on the operational models maintain dry weather
Monday, so high confidence in that part of the forecast. Trends also
push midweek precipitation farther south and mostly offshore.
Ensemble runs still show possible scenarios that bring precip into
our area midweek. Confidence in this part of the forecast remains
low.
Details...
Sunday night and Monday...
High pressure centered over Northern Ontario noses southeast over
New England, and should provide sufficient subsidence for mostly
clear skies. Mixing depth is forecast at 900 mb, with temps at that
level supporting max temps in the 30s. Clear skies, light wind, and
dew points in the teens should support Monday night min temps in the
mid teens to lower 20s.
Tuesday through Thursday...
As noted, a complicated pattern is being projected by the models.
There is a consistant trend of pushing the storm track farther
south, with all opertional models showing QPF mainly south of our
region. The GFS does show 6 hours of precip south of a Plymouth-
Providence line Tuesday afternoon. Also the ensemble members show
greater potential for precip reaching farther north, contrary to the
operational models. If there is any confidence in the model data, it
is in showing multiple storm segments passing us during this period.
Temperature profiles mostly support snow, expect for a rain-snow mix
Wednesday.
We have lowered pops a little, but maintain at least slight chance
pops in general and chance pops across southern RI and parts of
southeast Mass. This remains a low-confidence forecast, with all
scenarios...a complete miss, a South Coast special, or a broader
Southern New England event...continuing in play.
Friday...
High pressure builds over the region with dry weather and seasonably
cool temperatures.
&&
.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
Short Term /through Sunday/...High confidence.
Through this evening...
Mainly VFR. Although occasional light SHSN/SHRA possible mid
morning through mid afternoon with very brief MVFR/IFR
conditions. Winds W-NW shift to mainly NW late afternoon. Gusts
25-35 kt at times.
Tonight and Sun...
Mainly VFR with clearing. Winds also diminish this evening but
remain out of the NW.
KBOS Terminal...High confidence in TAF.
KBDL Terminal...High confidence in TAF.
Outlook /Sunday Night through Wednesday/...
Sunday Night through Monday: VFR. Breezy.
Monday Night: VFR.
Tuesday: VFR. Breezy.
Tuesday Night: VFR, with with areas of IFR possible on the South
Coast. Windy with gusts to 35 kt. Slight chance SN.
Wednesday: VFR, with areas IFR possible on the South Coast. Strong
winds with local gusts to 40 kt. Slight chance SN.
&&
.MARINE...
Short Term /through Sunday/...High confidence.
Today...
W-NW Gales continue through the day. mainly on the eastern and
ocean waters to the S of New England. These dissipate late this
afternoon and evening, with lingering Small Craft Conditions to
follow. Seas peak this morning 8-10 ft, and then begin to
diminish.
Tonight into Sun...
Winds seas diminish overnight such that a brief period with
conditions below Small Craft Advisory thresholds for a brief
period late into early Sun AM. The winds turn NW and pick up
25-30 kt during the day on Sun, sugggesting a need for Small
Craft Advisories to continue.
Outlook /Sunday Night through Wednesday/...
Sunday Night: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Areas of seas approaching 5 ft.
Monday through Monday Night: Winds less than 25 kt.
Tuesday: Low risk for Small Craft Advisory winds with gusts up to 30
kt. Seas locally approaching 5 ft. Slight chance of snow.
Areas of visibility 1 to 3 nm.
Tuesday Night: Moderate risk for gale force winds with gusts up to
40 kt. Areas of rough seas. Chance of snow, chance of rain, chance
of sleet. Visibility 1 to 3 nm.
Wednesday: Moderate risk for gale force winds with gusts up to 40
kt. Rough seas up to 11 ft. Chance of rain, chance of snow.
Areas of visibility 1 to 3 nm.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until midnight EDT tonight for ANZ232>235-
237.
Gale Warning until 6 PM EDT this evening for ANZ230.
Gale Warning until 8 PM EDT this evening for ANZ231-250-251-
254>256.
Small Craft Advisory until 6 PM EDT this evening for ANZ236.
&&
$$
SYNOPSIS...WTB/Doody
NEAR TERM...WTB/Doody
SHORT TERM...Doody
LONG TERM...WTB
AVIATION...WTB/Doody
MARINE...WTB/Doody